Standardize usage of virtual/override/final specifiers.

ash/system/tray/fixed_sized_image_view.h

Index: ash/system/tray/fixed_sized_image_view.h
diff --git a/ash/system/tray/fixed_sized_image_view.h b/ash/system/tray/fixed_sized_image_view.h
index 7a45961e4762c5e459882a979292b34a7693c4f8..abc2ed3c587cc38b656c66228f891dbd25354597 100644
--- a/ash/system/tray/fixed_sized_image_view.h
+++ b/ash/system/tray/fixed_sized_image_view.h
@@ -17,10 +17,10 @@ namespace ash {
 class FixedSizedImageView : public views::ImageView {
  public:
   FixedSizedImageView(int width, int height);
-  virtual ~FixedSizedImageView();
+  ~FixedSizedImageView() override;
 
  private:
-  virtual gfx::Size GetPreferredSize() const override;
+  gfx::Size GetPreferredSize() const override;
 
   int width_;
   int height_;